Laboratory experiments were conducted to determine green crab, Carcinus
maenas, consumption rates on and prey preferences among four bivalve species:
Olympia oysters (Ostrea coochaphila Carpenter), Japanese littleneck clams
(Venerupis philippinarum A. Adams and Reeve), bent-nosed macoma clams
(Macama nasuta Conrad). and California softshell clams (Cryptomya californica
Conrad) of different sizes. The bivalve size classes tested ranged in length from 10-14 mm
to 33-37 mm. Consumption rate and prey preference experiments were conducted by allowing
one starved (48 h) green crab (55-75 mm carapace width) to feed
ad libituni on bivalve prey for 16 h. All tests were conducted in 38-L aquaria
containing sand substrate 13 cm deep. A total of either 60 or 30 individuals of each prey
species were offered without replacement in each test. Mean green crab consumption rates
varied depending upon the prey species and size class. For bivalve prey of similar size,
Olympia oysters were consumed at a higher rate than bent-nosed macoma clams and Japanese
littleneck clams, while Olympia oysters and California softshell clams were consumed at
about the same rate. Green crabs preferred Olympia oysters to both bent-nosed macama clams
and Japanese littleneck clams by ratios ranging from 2:1 to 28:1. depending upon the prey
size. Small California softshell clams were preferred to small bent-nosed macoma clams by
a ratio of 8:1. The mean total biomass of Olympia oysters and bent-nosed macoma clams eaten
was 2.31 g
. d'-1. Our results show that green crabs are capable of consuming large quantities of
all four bivalve species tested. and that on bare sand substrate Olympia oysters are at
greater risk of green crab predation than bent-nosed macoma clams and Japanese littleneck
clams, and California softshell clams are at greater risk than bent-nosed macoma clams.